Carbon nanostructures have received a great deal of interest since their discovery. It has been suggested that carbon nanostructures may have important applications in electronics, in materials sciences, and in a number of additional fields. As used in this disclosure, a “carbon nanostructure” comprises a structure made up of chemically bonded carbon atoms, with or without impurities or intentionally added materials incorporated in the carbon structure or adjacent to the carbon structure. Carbon nanostructures include structures in which carbon atoms are arranged in generally a series of interconnected carbon arrays formed into a tube, cylinder, sphere, crystal, sheet or other structure. Carbon nanostructures may be single walled or multiple walled nanotubes, nanofibers, nanorope, spheres, crystals, or nanowire. Single wall nanotubes include a single layer of the hexagonally arranged carbon atoms, while multiple walled nanotubes are made up of an inner layer of carbon atoms and a series of one or more outer layers of hexagonally arranged carbon atom structures.
Despite the interest in carbon nanostructures and the potentially important uses for such structures, the practical application of carbon nanostructures in products has been slowed by the difficulty in manufacturing such structures. Two general types of processes have been employed to produce or isolate carbon nanostructures. One process type uses a plasma arc between carbon electrodes. U.S. Pat. Nos. 5,482,601 and 5,753,088 describe such carbon plasma arc processes for producing carbon nanotubes. Another process type involves simply isolating naturally formed carbon nanotubes from graphite and soot. Such an isolation process for carbon nanotubes is described in U.S. Pat. No. 5,560,898.
The paper “Monodisperse Carbon Nanopearls in a Foam-Like Arrangement: a New Carbon Nano-Compound for Cold Cathodes” by A. Levesque et al. discloses a process for manufacturing generally spherical carbon nanostructures having a diameter of approximately 150 nm. The process employed chemical vapor deposition using nickel nano-cluster-catalyzed dissociation of acetylene at 700° C. As reported in this paper, when the process was performed at 600° C., only carbon nanotubes were produced rather than spherical carbon nanostructures.
The prior processes for producing or isolating carbon nanostructures have been found to produce only small quantities of carbon nanostructures and/or produce carbon nanostructures of inconsistent quality. The low quality carbon nanostructures produced or isolated by the prior methods commonly included metal or other atoms incorporated in the carbon structure. These impurities incorporated in the walls of the carbon nanostructures may have a negative impact on the qualities and properties of the nanostructure and may render it unsuitable for an intended purpose. In particular, prior carbon nanostructure production techniques include no mechanism for preventing non-carbon atoms that may be present in a carbon-bearing feed material from being incorporated into the carbon nanostructure. Also, prior carbon nanostructure production techniques tend to allow carbon from the feed material to become incorporated into the carbon nanostructures in an unpredictable fashion outside of the desired interconnected carbon array structure. This inclusion of amorphous carbon in the resulting carbon nanostructure greatly degrades the properties and usefulness of the resulting carbon nanostructure.